Billah, M. R.

Blaicher, M.

Dalton, L. R.

Dietrich, P. I.

Elder, D. L.

Freude, W.

Harter, T.

Hoose, T.

Kieninger, C.

Koos, C.

Kutuvantavida, Y.

Lauermann, M.

Melikyan, A.

Muehlbrandt, S.

Randel, S.

Ummethala, S.

Wolf, S.

Zwickel, H.

English

KITopen

Hybrid Photonic Integration and Plasmonic Devices:  New Perspectives for High-Speed Communications  and Ultra-Fast Signal Processing C. Koosa,b,*, S. Randela, W. Freudea, L. R. Daltonc, S. Wolfa, C. Kieningera,b, Y. Kutuvantavidaa,b, M. Lauermanna, D. L. Elderc, S. Muehlbrandta,b, H. Zwickela, A. Melikyanb, T. Hartera,b,  S. Ummethalaa,b, M. R. Billaha,b, M. Blaichera,b, P.-I. Dietricha,b, T. Hoosea,b aInstitute of Photonics and Quantum Electronics (IPQ), Karlsruhe Inst. of Technology (KIT), 76131 Karlsruhe, Germany bInst. of Microstructure Technology (IMT), Karlsruhe Inst. of Techn. (KIT), 76344 Eggenstein-Leopoldshafen, Germany cUniversity of Washington, Department of Chemistry, Seattle, WA 98195-1700, United States *Email: christian.koos@kit.edu Abstract: Hybrid photonic integration allows to combine the complementary advantages of different material platforms while maintaining the processing and scalability advantages of monolithically integrated systems. Here we give an overview on our research in the field of hybrid integration, combining multi-chip approaches on a package level with hybrid on-chip integration using both back-end-of-line (BEOL) and front-end-of-line (FEOL) processes. OCIS codes: (230.2090) Electro-optical devices; (250.4110) Modulators; (130.3120) Integrated optics devices; (250.5300) Photonic integrated circuits; (250.5403) Plasmonics; (050.6875) Three-dimensional fabrication 1. Introduction Photonic integrated circuits (PIC) are key to a wide variety of applications, ranging from high-speed optical communications to metrology and sensing and further to ultra-fast signal processing. Over the last years, tre-mendous progress has been made in large-scale on-chip integration of optical devices, and several platforms have reached industrial maturity. However, these circuits mainly rely on monolithic integration concepts, where all devices are realized within the same material system. These enable highest scalability, but the performance of the resulting systems is often limited by the underlying material system. A prominent example is the silicon photonic (SiP) integration platform: From a technological point of view, silicon represents an excellent material system, enabling large-scale fabrication by mature CMOS processes along with monolithic co-integration of photonic and electronic circuits. From a functional point of view, however, silicon falls short of distinct proper-ties that are indispensable for a wide variety of devices. As a consequence, performance of all-silicon devices is often limited, e. g., in terms of speed, energy efficiency, or device footprint.  In this paper, we give an overview of our progress towards hybrid integration of photonic systems that combine the distinct advantages of different integration platforms while maintaining most of the processing and scalabil-ity advantages. To this end, we combine hybrid multi-chip integration on a package level with hybrid on-chip integration using both back-end-of-line (BEOL) and front-end-of-line (FEOL) processes.  2. Overview Regarding package-level hybrid integration, we have demonstrated that direct-write two-photon lithography lends itself as a viable tool for connecting photonic chips of different materials – either by three-dimensional (3D) free-form single-mode waveguides, so-called photonic wire bonds [1] – [4], or by facet-attached beam-shaping elements such as micro-lenses that allow for highly efficient coupling with relaxed alignment toleranc-es [5], [6]. We have demonstrated the viability of the concept by realizing multi-chip transmitter modules that combine silicon photonic modulators with InP-based laser-sources in highly integrated assemblies [7] [8]. To merge the advantages of different material systems in a BEOL approach, we have established the concept of silicon-organic hybrid (SOH) integration that combines silicon photonic waveguides with organic cladding ma-terials. By using theory-guided design principles, these organic materials can be tailored to provide functionali-ties complementary to those offered by the underlying SiP circuitry [9] – [12] . This approach is particularly well suited for overcoming the intrinsic absence of second-order nonlinearities in crystalline silicon by exploit-ing highly efficient organic electro-optic materials, thereby outperforming conventional all-silicon depletion-type pn-modulators both in terms of speed and energy efficiency [9]. SOH devices have been demonstrated to exhibit in-device electro-optic coefficients well above 300 pm/V, leading to voltage-length products down to 0.32 Vmm. This enables high-speed communications at peak-to-peak drive voltages as low as 140 mVpp, and energy consumptions of only a few fJ per bit [13]. The ultra-fast response of the electro-optic cladding materials enables small-signal modulation at frequencies beyond 100 GHz [14] and generation of on-off keying (OOK) data signals at 100 Gbit/s [15] [16]. We have further demonstrated generation of advanced modulation formats such as 16QAM at record-low energy consumption, and with symbol rates (bit rates) of up to 100 GBd (400 Gbit/s) transmitted on a single wavelength and a single polarization [17] – [19]. The extraordinarily low drive voltage of SOH modulators allows operation of the devices directly from standard output ports of field-programmable gate arrays (FPGA), without external amplifiers or digital-to-analog converters, even for genera-tion of higher-order modulation formats such as 16QAM [20]. SOH electro-optic modulators can also be used in optical metrology, enabling, e.g., high-performance frequency shifters that exploit the concept of single-sideband (SSB) modulation [21]. Note that the SOH approach is a versatile concept that goes far beyond electro-optic modulators. We have also demonstrated SOH lasers [22] that exploit doped light-emitting organic materi-als, as well as highly efficient SOH phase shifters with liquid crystals (LC) as a cladding [23].  Regarding hybrid FEOL integration, we combine semiconductor-based dielectric waveguides with metallic nanostructures that support plasmonic wave propagation. These devices feature ultra-fast carrier dynamics, thus enabling signal processing at THz bandwidths. More specifically, we have demonstrated the concept of plas-monic internal-photoemission detectors (PIPED) that exploit photon-generated hot carriers transmitted across potential barriers at metal-semiconductor interfaces [24]. The devices combine short carrier transit times with ultra-small parasitic capacitances and can hence be used as photomixers for generation and homodyne reception of continuous-wave radiation at THz frequencies [25]. Expanding upon our work on SOH devices, we have also shown that organic electro-optic materials can be combined with plasmonic waveguide structures [26] [27], thus merging BEOL and FEOL hybrid integration. While the length and the efficiency of these plasmonic-organic hybrid (POH) modulators is limited by optical losses, the devices stand out due to their small footprint and their large electro-optic bandwidth [9]. In summary, we believe that hybrid integration on different levels of optical systems allows to combine the dis-tinct advantages of different material systems and integration platforms. These apporoaches can hence pave the path towards photonic-electronic circuits for ultra-fast signal processing at THz bandwidths. 3. Acknowledgements This work was supported by the European Research Council (ERC Starting Grant ‘EnTeraPIC’, # 280145; ERC Consolidator Grant ‘TeraSHAPE’, # 773248), by the BMBF joint projects PRIMA (13N14630) and PHOIBOS (13N12574), by the H2020 Photonic Packaging Pilot Line PIXAPP (# 731954), by the Deutsche Forschungsgemeinschaft in the framework of the joint project “Hybrid integrierte photo-nisch-elektrische Systeme” (HIPES) and of the collaborative research center “WavePhenomena” (CRC 1173), by the Alfried Krupp von Bohlen und Halbach Foundation, by the EU-FP7 projects BigPipes and Phoxtrot, by the Helmholtz International Research School for Tera-tronics (HIRST), by the Karlsruhe School of Optics & Photonics (KSOP), and by the Karlsruhe Nano-Micro Facility (KNMF).  4.  References  [1] Lindenmann, N. et al.: ‘Photonic wire bonding: a novel concept for chip-scale interconnects;’ Opt. Express 20, 17667-17677 (2012)  [2] Lindenmann, N. et al.:‘Connecting silicon photonic circuits to multicore fibers by photonic wire bonding,’ J. Lightw. Technol. 33, 755 – 760 (2015) [3] Billah, M. R et al.: ‘Hybrid integration of silicon photonics circuits and InP lasers by photonic wire bonding’; arXiv:1802.03454 [physics.app-ph] (2018) [4] Hoose, T. et al.: ‘Connecting surface and edge emitting lasers to silicon chips,’ Optical Fiber Communication Conference (OFC'16), Los Angeles (CA), USA, March 20–24, 2016. Paper M2I.7 [5] Schneider, S. et al.: ‘Optical coherence tomography system mass-producible on a silicon chip’; Opt. Express 24, 1573-1586 (2016) [6] Dietrich, P.-I. et al.: „In-Situ 3D Nano-Printing of Freeform Coupling Elements for Hybrid Photonic Integration“; Nat. Photonics 12, 241 – 247 (2018) [7] Billah, M. R. et al.: ‘8-channel 448 Gbit/s silicon photonic transmitter enabled by photonic wire bonding,’ Optical Fiber Communication Conference (OFC'17), Los Angeles (CA), USA, March 19–23 , paper Th5D.6. (2017) [8] Billah, M. R. et al.: ‘Four-Channel 784 Gbit/s Transmitter Module Enabled by Photonic Wire Bonding and Silicon-Organic Hybrid Modulators’; 43rd European Conf. Opt. Commun. (ECOC'17), Gothenburg, Sweden, Sept. 17 –21 , paper Th.PDP.C.1 (2017) (Post-deadline paper) [9] Koos, C. et al.: ‘Silicon-Organic Hybrid (SOH) and Plasmonic-Organic Hybrid (POH) Integration’, J. Lightw. Technol. 34, 256-268 (2016) [10] Koos, C. et al.: 'Silicon-on-insulator modulators for next-generation 100 Gbit/s-Ethernet,' Proc. 33th European Conf. Opt. Commun. (ECOC'07), Berlin, Germany, September 16–20, 2007, paper P056 [11] Heni, W. et al.: ‘Silicon-organic and paslmonic-oragnic hybrid photonics,’ ACS Photonics 4, 1578 – 1590 (2017) [12] Jin, W. et al., ‘Structure–function relationship exploration for enhanced thermal stability and electro-optic activity in monolithic organic NLO chromophores,’ J. Mater. Chem. 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Technol. 33, 1210–1216 (2015)   [19] Lauermann, M. et al.: 'Low-power silicon-organic hybrid (SOH) modulators for advanced modulation formats,' Opt. Express 22, 29927–29936 (2014  [20] Wolf, S. et al.: "DAC-less amplifier-less generation and transmission of QAM signals using sub-volt silicon-organic hybrid modulators," J. Lightw. Technol. 33, 1425–1432 (2015)  [21] Lauermann, M. et al.: “Integrated optical frequency shifter in silicon-organic hybrid (SOH) technology”; Opt. Express 24, 11694 - 11707 (2016) [22] Korn, D. et al.: “Lasing in Silicon-Organic Hybrid (SOH) Waveguides”; Nat. Commun. 7, 10864 (2016)  [23] Pfeifle, J. et al.: 'Silicon-organic hybrid phase shifter based on a slot waveguide with a liquid-crystal cladding'; Opt. Express 20, 15359-15376, (2012)  [24] Muehlbrandt, S. et al.: ‘Silicon-plasmonic internal-photo-emission detector for 40  Gbit/s data reception’; Optica 3, 741-747 (2016)  [25] Harter, T. et al.: ‘Silicon-plasmonic integrated circuits for terahertz signal generation and coherent detection;’ arXiv:1802.08506 (2018) [26] Melikyan, A. et al.: 'High-speed plasmonic phase modulators,' Nat. Photonics 8 229–233 (2014).  [27] Melikyan, A. et al.: ‘Plasmonic-organic hybrid (POH) modulators for OOK and BPSK signaling at 40 Gbit/s’, Opt. Express 23, 9938 - 9946 (2015)  

Hybrid photonic integration and plasmonic devices: New perspectives for high-speed communications and ultra-fast signal processing

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Hybrid photonic integration and plasmonic devices: New perspectives for high-speed communications and ultra-fast signal processing

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